Flying After Diving:

History, Research & Guidelines Richard Vann, Ph.D.

Research Director Divers Alert Network DEMA 2002 Las Vegas 1

1961 – 1

st

Report



Cabin altitude 8-10,000 ft



Pilot & copilot were incapacitated



Flew <4 hrs after diving to <30 fsw



Flight engineer was less severely affected and landed the aircraft



Flew ~12 hrs after diving - Miner (1961) Flight Safety Foundation J - Blumkin (1991) FSFJ 38(5):1-5 2

1967 – 1

st

Animal Study



Dives: 53-88 fsw for 7 hrs



PFSI: 1, 3, 6, or 12 hr



Altitude: 10K ft for 2 hrs



Results:



93% DCS with 1 hr surface interval



No DCS with 12 hr surface interval - Furry et al. (1967) Aerosp Med 1967;38(8):825-28 3

4

1969 – 1

st

Human Study



Dives: 40 fsw/200 min; 120 fsw/15 min



SI: 5 min, 30 min, 1 hr, 2 hrs, or 3 hrs



Altitude: 8K ft/112 min & 16K ft/5 min



Results: in 41 exposures at



2 hrs, 1 DCS at 8,000 ft & 9 DCS at 16,000 ft



Application: basis of 2 hr USN FAD rule for single no D dives from ‘85-99 - Edel et al. Aerosp Med 1969;40(10):1105-10

1982 - Direct Ascent Study

5 Altitude: 10K/4h-16K/1h; 8.5K/4h-14K/1h D (fsw) 11 40 60 80 100 T (min) 1440 34 20 14 10 DCS 1 @16K Exposures USN RG 1 @16K 2 @14K,16K 1 @10K 1 @16K 20 20 36 35 38 H E D D D 130 7 0 20 D - Bassett (1982) USAF SAM Report

FAD Situation in 1970s-80s

6



Sparse data from manned testing

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>30 guidelines published since 1980

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0 - 24 hr range for PFSI



Controversy between advocates of



Maximum dive time & PFSI = 0-4 hrs



Zero DCS & PFSI



24 hrs

UHMS FAD Workshop

24 Feb 89



Literature review



Fundamental issues of decompression



FAD research



Expert opinion 7

UHMS FAD Workshop Recreational Diving Guidelines Type of Diving



No-D diving (<2 hr/48 hrs)



No-D multi-day diving



D-stop diving PFSI 12 hrs 24 hrs 24-48 hrs 8

More Controversy



DAN & certifying agencies revised all guidelines to 24 hrs



Skin Diver Magazine took exception arguing 24 hrs was not justified by the low incidence and hotels and dive operators would lose money 9

1991 Resolution



Jun 91 UHMS, DAN, certifying agencies met



1991 DAN revised recommendations



Type of Diving SI (hrs)



No-D diving



No-D multi-day diving 12 hr minimum or D-stop diving >12 hr 10

Proportion of Divers Who Fly 40% 30% % Who Flew Unpressurized or by Commercial Air 20% 10% Project Dive Exploration 369 379 269 759 268 434 391 459 566 591 465 508 Diving Injuries 483 451 430 591 729 232 11 0%

1986 1988 1990 1992 1994 1996 1998 2000 2002

Year

Divers with Symptoms Before Flying



From 1998 to 2000, 278 injured divers were involved with flying after diving



Of these, 55% had symptoms before they flew



This is an educational problem: divers are not recognizing their symptoms 12

FAD Affects DCS Severity

13 49% % of Divers with Residual Symptoms after All Treatments from 1989 2000 50% 40% 30% 20% 10% 0% 46% p<0.0001

32% Flew with Sx Sx In-Flight All Others



The incidence of any residual symptoms after all treatments was 14-17% greater for divers who flew than for divers who did not fly

PFSI & Recreational Diving

14



Does PFSI affect DCS risk after repetitive, multi-day diving?



We don’t know the PFSIs for the entire population, but we have data for



382 injured divers (no preflight Sx)



245 injury-free controls from Project Dive Exploration

Case-Control Study



Can’t estimate absolute injury rates without the entire population



Can estimate the relative risk of one condition compared with another



Is the relative risk at short surface intervals greater than at longer surface intervals?

- Freiberger et al., ASEM 2002; 73:980.

15

30 25 Preflight Surface 20 15 Interval (hrs) 10 5 0 Average PFSI 27.1

Injury Free Controls 20.7

Injury Cases 16

60% 50% 40% 30% 20% 10% 0%

PFSI Distribution

382 Injured Divers 245 PDE Divers <12 12-24 24-36 36-48 Surface Interval (Hrs) >48 17

Relative Risks



Increased relative risk of DCS for



shorter surface intervals

–

gradual increase for SIs from 24



12 hrs

–

steep increase for SIs from 12



0 hrs



deeper dives on the last day of diving



Define Relative Risk = 1 for



24 hr surface interval



60 fsw maximum depth on last dive day 18

PFSI & Relative Risk

15 12 100' 9 6 3 0 0 60' 30' 130' max depth on last dive day Relative Risk = 7 Relative Risk = 1 10 20 30 Surface Interval (hrs) 40 19 50

In-Flight Pain & Neuro Sx at

20

26 Hrs After Diving

5-8,000' estimated Time (hrs) flight altitude 0 24 48 72 96 Depth 0 (fsw) 50 100 150

PFSI & Absolute Risk



Estimate PFSIs that have low DCS risk after no-decompression dives near the recreational exposure limits



Chamber study



1993 to 1999 21

Experimental Design

22 Dive Flight Decrease the PFSI and observe the change in DCS incidence PFSI (3-17 hrs) 8,000 feet for 4 hours

DCS Severity



Mild DCS



limb pain, localized abnormal sensation



Moderate DCS



sensory deficit, weakness



Serious DCS



paralysis, difficulty breathing, fainting, cerebral dysfunction, death 23

Sequential Design



Accept a surface interval if only a “few” mild DCS incidents occur.



Test a shorter interval.



Reject a surface interval if “too many” mild DCS incidents occur or if DCS is moderate or serious.



Test a longer surface interval. 24

Recreational Dive Planner (RDP) 25 -start-up funding provided by PADI

RDP FAD Procedures



Wait 4 hrs after one no-D dive of less than 60 min



Wait 12 hrs after one no-D dive of more than 60 min or after repetitive dives



Wait 24 hrs after emergency decompression 26

Single Dive Profiles



40' for 60 min



40' for 120 min



60' for 55 min*



100' for 20 min* * Recreational Dive Planner (RDP) limit 27

Repetitive Dive Profiles

28



40'/60 min -1 hr SI 40'/60 min



60'/55 min -1 hr SI 60'/20 min*



60'/55 min -1 hr SI 60'/20 min -1 hr SI 60'/20 min*



100'/15 min -1 hr SI 60'/35 min* * Near RDP limits

Results



802 FAD exposures



40 DCS incidents (5%)



21 Moderate DCS



18 Mild DCS



1 Serious DCS 29

30

Single Dives (n=344)

20 15 10 DAN 40'/60min 40'/120min 60'/55min 100'/20min RDP 5 USN 0 2 USAF 4 6 8 10 12 14 16 18 20 Preflight Surface Interval (hours) 22 24

Repetitive Dives (n=458)

20 15 10 100'+60' 60'+60' 60'+60' +60' 40'+40' PADI=12 hrs 31 5 DAN “>12 hrs” USAF 0 2 4 6 8 10 12 14 16 18 20 Preflight Surface Interval (hours) 22 24

FAD Trials Summary



No DCS for single dives less than 60 min at PFSIs of 11 hrs or more



No DCS for repetitive dives at a 17 hr PFSI



Results apply only to the dive profiles tested with dry, resting divers 32

1999 USN FAD Rules



Why change?



Duke studies indicated that a 2 hour PFSI was too short



Need to perform low level flights as soon as possible after a dive



Need procedures to allow further ascent to altitude after performing a dive at altitude 33

1999 USN Dive Manual

34

RG

I

C

F K

Z

1999 USN FAD Rules

SI Before Ascent to Altitude 1,000' 4,000' 8,000' 10,000' 0:00 0:00 0:00 3:00 8:17 0:00 0:00 5:15 8:20 13:37 0:00 9:43* 15:58* 19:03* 24:00 8:26 19:07 24:00 24:00 24:00 * based on DAN trials 35

36 25 20

USN Guidelines at 8,000'

1999 USN Guidelines DCS No DCS Bassett (direct ascent) 15 10 5 0 A B C D E F G H I J K L M USN Repetitive Group Designator N O Z

Fleet Feedback



Procedure is too complex



Prefer simple 12 or 24 hour rule



Procedure is too restrictive



Prevent some working on waterfront from going home to mountains after work



Desire to return to 2300 foot unlimited ascent rule 37

38 May 2002 Workshop: Revised Recreational FAD Guidelines



Are any FAD guidelines needed at all?



Are current FAD guidelines acceptable?



What is the longest PFSI needed after multi-day, repetitive diving at the limits of the recreational dive tables?

2002 FAD Workshop: Consensus Recommendations (1) 39



Apply to air dives followed by flights at cabin altitudes of 2,000 to 8,000 feet for divers who do not have symptoms of DCS



Recommendations should reduce DCS risk but do not guarantee avoidance



Longer preflight surface intervals will further reduce DCS risk

2002 FAD Workshop: Consensus Recommendations (2) 40



Dives within the No-D Limits



Single No-D Dive: a minimum preflight surface interval of 12 hours is suggested



Multiple Dives per Day or Days of Diving: a minimum preflight surface interval of 18 hours is suggested



Dives Requiring Decompression Stops



Little experimental or published evidence



A preflight surface interval substantially longer than 18 hrs appears prudent



NASA O

2

FAD Tables

NBL dive profile – 40 fsw for 240-390 min 41

 

Breathing gas – nitrox (46% O 2 ) Dry suit (EMU) – pressurized to 4.0 psid



Equivalent Air Depth – 23.9 fsw *NBL - Neutral Buoyancy Laboratory, Johnson Space Center, Houston *EMU - Extravehicular Mobility Unit (standard U.S. 'space suit')

FAD Limits (Nitrox) - EAD=25 fsw Duration (min) 1-45 46-80 81-290 291-400 Air PFSI (hr) (USN PFSI) 3 (8:26) 5 (16:18) 14 (24:00) 24 (24:00) Oxygen PFSI (hr) 0.33

0.67

2 3 42 Cabin altitude <10,000 ft MSL No flight restrictions > 24 hr post-dive

Operational Experience



Anecdotal – no database



Average 3-5 individuals annually



PFSI of 4-18 hours



No cases of DCI 43

On-Going USN FAD Study

44



Evaluate untested USN FAD guidelines including decompression dives



Evaluate effectiveness of post-dive O 2 breathing in reduce PFSI



Use echocardiography to search for arterial bubbles in the heart



Three year project with 500-700 subjects

Come Dive and Fly with Us 45